This application is based upon Japanese Patent Application No. 2000-229112 filed on Jul. 28, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus and method for controlling a motor-driven cooling fan for a vehicle.
2. Related Art
A vehicle (for example, automobile) is provided with a cooling fan for cooling a radiator of an engine and a condenser of an air conditioner. The cooling fan is conventionally rotated by a motor (for example, DC motor). FIG. 7 schematically shows an electric configuration of a cooling fan control system. A fan control system 1 includes a DC motor 3 for rotating a cooling fan 2 and a motor control unit 4 for controlling a voltage applied to the DC motor 3.
The motor control unit 4 receives a control signal Sa as a motor application voltage instruction from an engine control unit 5, and operates on a power supplied from a battery 6. An input processing circuit 7 is an interface circuit for receiving the control signal Sa, converts the control signal Sa into a voltage instruction signal Sb, and outputs the voltage instruction signal Sb to a driving circuit 8. On the basis of a voltage applied to the motor 3 (motor application voltage) detected by a motor voltage detecting circuit 9 and an instructed voltage indicated by the voltage instruction signal Sb, the driving circuit 8 controls a gate voltage of an MOSFET 10 so that the motor application voltage becomes equal to the instructed voltage.
When the motor 3 is driven by the motor control unit 4 to rotate the cooling fan 2, air is blown. The blown air passes through a condenser 11 and a radiator 12, thereby cooling the condenser 11 and the radiator 12. Since the cooling fan 2, condenser 11, and radiator 12 are disposed in the front portion of the automobile, air flowing (flowing air) in association with the driving of the automobile also passes through the condenser 11 and radiator 12, thereby contributing to the operation of cooling them.
The engine control unit 5 receives an engine cooling water temperature signal, an ON/OFF signal (clutch signal) of a magnet clutch for transmitting the engine power to the compressor of the air conditioner, and a refrigerant high pressure signal indicative of an increase in the pressure of a refrigerant, controls the engine by using the signals, and outputs the control signal Sa to the motor control unit 4. The clutch signal becomes ON state (high level, for example) when the heat exchangeability of an evaporator of the air conditioner decreases. The refrigerant high pressure signal becomes ON state (pressure increased state) when the refrigerant pressure increases to a reference value or more due to insufficient cooling of the condenser 11 or high load operation of the compressor. Alternately, a motor control circuit, which has the function of directly receiving the signals, not via the engine control unit, and generates an application voltage instruction to the DC motor 3 based on the signals, may be used.
FIG. 8A shows the motor application voltage instructed to the motor control unit 4 by the engine control unit 5. The horizontal axis indicates the temperature of engine cooling water and the vertical axis expresses motor application voltage ratio (%). The engine control unit 5 instructs the motor control unit 4 to increase the motor application voltage step by step or at a predetermined rate in accordance with an increase in detected temperature of the engine cooling water.
In the example, when the magnet clutch is turned on so that the compressor is in a driving state, the engine control unit 5 instructs the motor control unit 4 to set the motor application voltage so as to be 50% or more. Further, when the refrigerant high pressure signal becomes ON state, the engine control unit 5 instructs the motor control unit 4 to set the motor application voltage so as to be 70% or more. The value (50%, 70%) of the motor application voltage instructed here varies according to a vehicle.
Generally, the operation of the cooling fan 2 is mostly requested by the air conditioner system. As described above, in the conventional cooling fan control system, when the compressor is driven, the application voltage of at least 50% is applied to the DC motor 3. Consequently, the compressor and the cooling fan 2 operate almost synchronously with each other as shown in FIG. 8B.
However, during the driving of the automobile, air flows through the condenser 11 and radiator 12. The flowing air also contributes to cool the compressor and the radiator. Even in such a case, conventionally, the DC motor 3 is driven according to the control pattern shown in FIG. 8A without considering the air flow. As a result, the power of the battery 6 is consumed in vain.
The invention has been achieved in consideration of the circumstances and its object is to provide an apparatus and method for controlling a motor-driven cooling fan for a vehicle, with reduced power consumption of the motor while assuring a necessary cooling air.
According to a first aspect of the invention, in a state where the voltage applied to a motor is controlled to be a predetermined voltage by which an air volume required for cooling is obtained, control means detects a current flowing the motor. The current flowing the motor is reduced when a load on the motor decreases, that is, when the flowing air is given to a cooling fan for vehicle as a vehicle travels for the reason that the flowing air contributes to the cooling.
Consequently, when the decrease in the current flowing the motor is detected, the control means sets the voltage applied to the motor so as to be lower than the predetermined voltage by an amount corresponding to the cooling capability by the flowing air and controls so that the required cooling air volume is assured as a total of the cooling air generated by the cooling fan and the flowing air. As a result, the power required to assure the required cooling air volume can be reduced. For example, the power of a battery mounted on the vehicle can be saved.
According to a second aspect of the invention, when it is detected that the current flowing the motor is lower than a current flowing the motor at the time of vehicle stop by a predetermined amount in a state where the voltage applied to the motor is controlled to be a predetermined voltage, the control means changes the application voltage. With the configuration, for example, the voltage is changed after the vehicle travels and the flowing air by which the power saving of a certain degree can be expected is obtained. Thus, the voltage applied to the motor can be prevented from being controlled to be excessively low.
According to a third aspect of the invention, by detecting a decrease in the current flowing the motor, the control means detects whether the flowing air at the required cooling air volume or higher is obtained. When the flowing air has the required cooling air volume or more, the control means changes the application voltage. In this case, the necessary cooling can be achieved only by the flowing air, so that the control means can stop the passage of current to the motor.
According to a fourth aspect of the invention, when the application voltage is changed, the control means sets the voltage applied to the motor to a voltage with which the motor can rotate. When the voltage applied to the motor is low and the motor does not rotate, a fluctuation in the load by the current flowing the motor (change in the air volume) cannot be detected. With the configuration, the motor continuously rotates, so that the control can detect the state of the flowing air also after the application voltage is changed and can change the application voltage as necessary.
According to a fifth aspect of the invention, by detecting an increase in the current flowing the motor in a state where the voltage applied to the motor is controlled to be the predetermined voltage, the control means detects that the load on the motor increases, that is, the flowing air passing through the cooling fan for a vehicle decreases. When the increase in the current flowing the motor is detected, the control means makes the voltage applied to the motor higher by an amount corresponding to the decrease in the flowing air, and controls so that the required air volume is assured as a total of the cooling air generated by the cooling fan and the flowing air.
Consequently, in an actual operating state where the vehicle repeatedly stops and travels, not only in the case where the flowing air increases but also in the case where the flowing air decreases, the motor power consumption is reduced by using the flowing air according to the operating state.
According to a sixth aspect of the invention, current change detecting means outputs a current decrease signal when the current flowing the motor becomes lower than a threshold value, that is, when the air volume of the flowing air larger than the air volume corresponding to the threshold value passes through the cooling fan so that the load on the motor decreases. The voltage control means decreases an instruction voltage when the current decrease signal is output, and controls the voltage applying means so that the voltage applied to the motor coincides with the instruction voltage.
When the air volume of the flowing air passing through the cooling fan becomes equal to or lower than the air volume corresponding to the threshold value, the current decrease signal is not output. The voltage control means uses a predetermined voltage applied from an outside as an instruction voltage and controls the voltage applying means so that the voltage applied to the motor coincides with the instruction voltage. As a result, as compared with the conventional configuration in which the motor is rotated on the constant voltage irrespective of the flowing air, the power consumption of the motor can be reduced.
According to a seventh aspect of the invention, in a manner similar to the means in the third aspect, the voltage control means decreases the instruction voltage in the case where the required air volume can be assured by the flowing air. In this case, the voltage control means can set the instruction voltage to zero, that is, can stop the passage of the current to the motor.
, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings.